In the majority of applications for industrial gases, it is necessary to have the gas available at a relatively high pressure, generally of the order of 8 to 14 bars, in a distribution circuit. With many gases, when the throughputs involved are considerable it is usual to have a store of gas in the liquified state at low temperature and to evaporate it as demand requires. At the present time, this evaporation takes place at the high distribution pressure by heating either with purely atomspheric heaters or with auxiliary energy supply means. Whatever the methods of heating, in such a case the whole of the distributing circuit and the storage tank are thus at all times maintained at the high distribution pressure, which makes it necessary for the storage tank to be designed for this high pressure. Designing the tank in this way proves particularly costly in the case of cryogenic tanks which are formed by two shells which leave between them an insulating space under high vacuum with a filling of an insulating material such as "perlite". The result is that the inner shell has to be made of a pressure-resistant material. Installations of this kind are generally replenished at regular intervals by specialised vehicles fitted with transfer means such as pumps which allow the cryogenic liquid to be transferred from the low pressure tank carried by the vehicle to the high pressure distribution storage tank. This calls for a large outlay on means for pressurising the liquid together with a by no means neglible expenditure of energy for the transfer.
There has already been proposed a method of distributing gases at high pressure in which there is a stored volume of a gas available in the liquid state at low pressure, a portion of the said stored volume being extracted when the distribution pressure falls below a threshold value and being transferred to a confined enclosure at the said low pressure in which all communication between the said confined enclosure and the said stored volume is cut off and in which the distribution circuit at high pressure is placed in communication with the said enclosure. In this proposal, the confined enclosure is thermally insulated from the exterior and the communication with the distribution circuit is made by simultaneously balancing the pressure both in the gaseous phase and in the liquid phase in the confined enclosure, and the cryogenic liquid drains by gravity to a heating evaporator. Such an arrangement, although it enables the above-mentioned drawbacks to be overcome by allowing the storage tank to be designed for a low storage pressure, is relatively complex since it means not only that the confined enclosure has to be situated below the storage tank but also that the heating evaporator too has to be below the confined enclosure, which is a serious disadvantage from the point of view of bulk. Furthermore this arrangement, in addition to making it necessary for the confined enclosure to be thermally insulated, also requires a double connection to the heating evaporator through piping and valves. In addition, the draining of the liquid from the confined enclosure to the heating evaporator simply by gravity is a relatively time-consuming process.
It is an object of the invention to provide a method for distributing gases under pressure which is quickly put into effect, and also apparatus for carrying out this method which is small in bulk and of simple and inexpensive design.